1. Field of the Invention
The present invention relates to the field of biometrics. More specifically, the present invention relates to live scanning of prints.
2. Background Art
Print imaging systems can capture images of prints on thumbs, fingers, palms, toes, feet, and/or hands. Such print imaging systems are also referred to as live scanners, live print scanners, or simply scanners. Live scanners often include a light source, platen and camera. An object having a print pattern is placed on the platen. A platen is often one planar surface of a prism. The light source illuminates the platen. The camera captures an image of a print placed on the platen.
Many live print scanners utilize the optical principle of frustrated total internal reflection (TIR) to capture a high-quality image of a print pattern. Such a print pattern includes ridges and valleys that make up all or part of a print. For example, ridges on a finger can operate to alter the refraction index at a platen surface compared to valleys, thereby interrupting the TIR of light at the platen surface. This interruption in the TIR causes a high quality optical image representative of the ridges and valleys of a print pattern to be captured by a camera.
One problem with conventional palm live scanner systems is that a palm naturally curves, while a typical platen has a flat planar surface upon which a palm is placed. Thus, there is a chance that not all portions of the palm print, especially the pocket in a center of a palm, will be imaged during scanning. If this occurs, a “dead spot” can occur at the palm pocket and biometric information can be lost.
Another problem is the difficulty in capturing an image of a print pattern on the outer edge of the palm located opposite the thumb (also called the writer's palm). When a palm is placed on a planar platen, the print pattern of the writer's palm does not contact the platen surface; rather, it extends upward away from the platen. As a result, the print pattern on the side of the palm including the writer's palm can only be captured in a separate scan from the scan of the main palm itself. Two scans is expensive, more complex, and burdensome to palm print scanner users.
Attempts have been made to provide a convex or non-planar platen that better fits the shape of a palm pocket. See, U.S. Pat. Nos. 5,526,436 and 5,528,355. Such attempts, however, do not overcome the above-mentioned problems.